The invention relates to a method and apparatus for ultrasound imaging of a biopsy needle or the like during an ultrasound imaging examination, including the steps of alternately performing one or more imaging scans with ultrasound transmit and receive parameters which are adapted for optimized imaging and visualization of the needle and one or more imaging scans with ultrasound transmit and receive parameters adapted for optimized imaging and visualization of the body or details thereof, in which the needle is inserted.
This method is used to monitor the position of a biopsy needle inside the human body, before removing a sample of tissue. The needle and the surrounding tissue are imaged in real time for an easier control of the needle orientation and proper depth, to remove the tissue from the predetermined location. Obviously, the best position of the needle is the one in which both the instrument and the tissue are best imaged. Unfortunately, the tissue and the instrument are reflectors having totally different characteristics, which require different settings of ultrasound imaging parameters. This is also due to the fact that the needle is a specular reflector, i.e. reflects ultrasonic waves like a mirror. Hence, as the distance from the ultrasound beam incident on the needle to the perpendicular of the needle increases, the energy reflected toward the probe decreases. Nevertheless, these conditions contrast with the optimized setting conditions for tissue imaging.
U.S. Pat. No. 5,836,882 discloses a method and an apparatus for localizing a tip of a probe inside a biotic structure. The apparatus includes a probe with an ultrasonic transmitter attached proximate a tip of an insertion end of the probe. The apparatus further includes a color Doppler ultrasonic imaging system coupled to a sonifying transducer and a speaker coupled to the ultrasonic imaging system which reproduces sound information indicative of a position of the probe relative to the sonifying transducer.
EP 0 278 993 deals with a concentric biopsy probe. An ultrasound imaging probe suitable for concentric on-axis biopsy procedures includes an aperture through which a biopsy needle is inserted to sample a target tissue previously located by the ultrasound probe. In operation the ultrasonic probe is first positioned on the subject over target tissue A cursor is moved to visually overlap the target tissue within the subject, an the depth is indicated on a corresponding display. A biopsy needle is selected and adjusted to extend to the indicated depth when inserted through the ultrasonic probe and transducer aperture into the subject. Thus the apparatus provides for the source aperture, used for imaging, thus minimizing risk and error arising from conventional off-axis needle entrances.
U.S. Pat. No. 6,048,312 and EP 952,462 disclose methods and apparatuses which allow imaging of the needle and tissue during an ultrasound imaging session. According to the methods disclosed in these documents imaging is performed in the B-mode or Doppler or Color Doppler modes, wherein the ultrasound beam firing parameters are alternately modified for optimized imaging of the needle and of surrounding tissues. Then, the images acquired thereby are combined to obtain a single image in which the needle and the surrounding body are both displayed.
While tissue imaging parameters are well-known and widely used, the above documents suggest that the needle is imaged by suitably deforming or steering the beam transmitted by a probe, which is particularly linear, so that the angle of incidence between the beam and the needle is perpendicular to the needle or as close as possible to this condition. The two above mentioned documents are to be intended as parts of the following disclosure, even as an explanation of the detailed technical aspects of this invention.
However, it often happens that the tissue wherefrom a sample is to be removed, for instance a cyst or tumor tissue, is characterized by an increased circulation, i.e. by an increased blood flow thereto. Therefore, there is an interest in imaging body fluid flows, particularly vascular flows, rather than static tissues. Unfortunately, body fluids have such characteristics that they cannot be easily displayed by using traditional ultrasound imaging techniques. Body fluids are worse reflectors as compared with static tissues, hence their imaging contribution is several orders of magnitude smaller than that of static tissues, i.e. body flows are essentially anechogenic, whereas static tissues are echogenic or hyperechogenic. Hence, specific techniques have been developed to allow selective optimized imaging of body fluid flows as opposed to static tissues, which techniques are divided into two main branches. Invasive techniques are those in which contrast agents are injected in the region under examination, i.e. agents consisting of microbubbles which are carried by body flows and have a non linear reflection behavior, i.e. reflect the ultrasound beams, which have been transmitted at a certain fundamental frequency, at a harmonic or sub-harmonic of the fundamental frequency of the ultrasound beams transmitted to the body under examination. In this case, since static tissues have a linear reflection behavior, by only detecting the beams reflected at a selected harmonic or sub-harmonic frequency the imaging contribution of body fluids may be differentiated and isolated. Here, the transmit and receive parameters are still different from those required for optimized imaging of the needle and the static tissues surrounding it.
An alternative fluid flow imaging technique consists in using the phase shift introduced in the reflected beams by body fluids with respect to static tissues. In fact, the particles which form body fluids are in motion, unlike the particles of essentially static tissues, and determine a phase shift between the reflected beams and the incident beams, whereas essentially no phase shift occurs for beams reflected by static or quasi static tissues. Hence, by providing two successive imaging procedures, with identical transmit and receive parameters, and by directly subtracting the received signals of the two imaging procedures, imaging contributions having the same phase are removed or drastically reduced, whereas all imaging contributions which have had a phase shift are maintained.
Hence, the transmit and receive parameters for body flow imaging are different from those optimized for imaging the needle and the surrounding tissues, both as regards the imaging frequency and the imaging method and as regards the transmission intensity of the ultrasound beams for illuminating the body under examination. In fact, it is known that, in order to avoid the mechanical collapse of contrast agent microbubbles, the intensity of incident ultrasound beams has to be reduced to limit the mechanical index and control or prevent as much as possible the collapse of contrast agents.
The techniques disclosed by U.S. Pat. No. 6,048,312 and EP 952,462 do not address the need to not only monitor the needle and the surrounding tissue but also body fluid flows for a proper and more accurate location of the biopsy site position, and do not even disclose a method to do this and an apparatus for implementing the method, especially allowing real time imaging. The real time imaging feature should not be underestimated, since the patient is in an invasive treatment condition, with a needle inserted in his/her body, and the removal operation has to be as fast as possible to avoid any trouble or other inconvenience.
Therefore, the invention has the object of providing a method and an apparatus for ultrasound imaging of a biopsy needle or the like, which provides a higher capability for an optimized imaging of the needle and of the body in which the latter is inserted.
The invention achieves the above purposes by providing a method and an apparatus for ultrasound imaging of a biopsy needle or the like, during an ultrasound imaging examination as described hereinbefore, which includes the step of injecting contrast agents in the region under examination, and in which the ultrasound transmit and receive parameters adapted to optimized imaging and display of the body or details thereof, in which the needle is inserted, are parameters optimized for imaging body fluid flows.
Particularly, the ultrasound transmit and receive parameters optimized for imaging fluid flows involve the transmission of ultrasound beams at the fundamental frequency and with a low mechanical index, i.e. at a low intensity and the reception of ultrasound reflected beams at a harmonic or sub-harmonic frequency, particularly at the second harmonic of the fundamental frequency of transmitted beams.
In combination with the above, the invention provides alternate ultrasound imaging with transmit and receive parameters optimized for imaging the needle, with transmit and receive parameters optimized for imaging the tissues of the body under examination or a detail thereof, and with transmit and receive parameters optimized for imaging body fluid flows.
It shall be noted that alternate imaging is intended to mean that, within the same section of the imaged body, one or more images or frames are respectively acquired for transmit and receive parameters optimized for imaging the needle, tissues, or body fluid flows. Here, it is possible to properly account for the transmit beam firing repetition times.
The images obtained by the above imaging procedures with transmit and receive parameters optimized for imaging the needle or body fluids and possibly for tissues may be displayed with well-known techniques, i.e. by assigning different color scales and/or gray scales to the intensity values of the reflected beams, and by combining the images together, i.e. by overlaying the different images of the needle, the body flows and/or possibly tissues.
As an alternative thereto, images may be displayed in adjacent and separate positions or with different image sub-combinations, such as a combination of images of the needle and of tissues in adjacent positions, and a combination of images of the needle and of body fluid flows, or other possible sub-combinations.
According to an embodiment of the method, the invention provides an imaging procedure with a low mechanical index and at the second harmonic for imaging body fluid flows and an imaging procedure with a low mechanical index and at the fundamental frequency with needle optimized parameters, for instance by using a steering technology in the case of linear probes.
An alternative embodiment provides an imaging procedure with a low mechanical index and at the second harmonic for imaging body fluid flows and an imaging procedure with a high mechanical index and at the fundamental frequency with needle optimized parameters, for instance by using a steering technology in the case of linear probes.
Another alternative embodiment provides an imaging procedure with a low mechanical index and at the second harmonic for imaging body fluid flows and an imaging procedure with a high mechanical index and at the fundamental frequency, with needle optimized parameters, for instance by using a steering technology in the case of linear probes, as well as an imaging procedure with a high mechanical index and at the fundamental frequency with tissue optimized parameters.
Yet another alternative embodiment provides an imaging procedure with a low mechanical index and at the second harmonic for imaging body fluid flows and an imaging procedure with a high or low mechanical index and at the fundamental frequency, with needle optimized parameters for instance by using a proper steering technique in the case of linear probes, as well as an imaging procedure with a high mechanical index and at the second harmonic frequency, with tissue optimized parameters.
A variant embodiment provides a first imaging procedure at the second harmonic optimized for imaging body fluid flows and another imaging procedure with a high or low mechanical index and at a fundamental or second harmonic frequency, which subtracts two successive reflection echoes determined by two successively fired ultrasound beams for imaging the needle. The parameters of one of these two ultrasound beams are the same as the paraemeters of the other one of these two ultrasound beams.
The different imaging procedures may be executed alternately, within a predetermined frame rate, or parallel to each other, i.e. simultaneously at least as regards processing, there being provided two or three dedicated receive and processing chains.
The different variant embodiment as disclosed above may be provided in combination with three-dimensional imaging methods.
Particularly, a preferred three-dimensional imaging method includes the following steps:                transmitting ultrasound beams, generated by transducers, into a volume under examination, corresponding to a body under examination or a part thereof; receiving and storing the signals generated by the ultrasound beams in said volume under examination; processing the received signals into image data associated to image dots or lines of a display; displaying at least a portion of image data on the display according to user selected parameters, relating to a predetermined image section or projection plane of said volume under examination, the processing of ultrasound beams and/or the display being predetermined in a targeted manner, with reference to a previous selection of an image section or projection plane of the volume under examination to be imaged and which method comprises the additional steps, i.e.:        defining a virtual volume which coincides with the body or the part thereof under examination or a three-dimensional reference system, which have a precise orientation with respect to the scan planes generated by the ultrasonic probe; selecting the section plane of the body under examination and/or of the part thereof along which ultrasonic imaging is to be performed; determining the coordinates of the dots which form said section plane along which imaging is to be performed with reference to the virtual volume; limiting the scan to the area which coincides with said section plane along which imaging is to be performed; transmitting and receiving transmit signals and reflection echoes, only relating to the lines of view of the probe which coincide with the projection surface or band of the selected section plane along which imaging is to be performed; processing and displaying only the received echo signals.        
As shown above, the method involves the combined display of the images acquired by optimized imaging for the needle, body fluid flows and/or possibly for tissues. Further, the different images may be appropriately colored in a desired manner to allow an optimized interpretation by the personnel charged with diagnostic evaluation.
The method of the invention provides alternate and successive transmission of ultrasound beams with parameters optimized for imaging the needle, body fluid flows and/or possibly tissues respectively according to the above disclosure and parallel processing of the received data, and has one, two or possibly three separate processing chains, which are set for receiving and processing the echoes deriving from the two or possibly three types of parameters of the transmitted ultrasound beams.
In this case, the parameters which control the optimized transmission for imaging the needle, body fluid flows and/or stationary tissues may be contained in a memory of the apparatus.
Hence, the method provides the automatic modification of the transmit parameters based on the number of scans of the region under examination assigned to optimized imaging of the needle, of fluids and/or of tissues respectively.
The number of images to be acquired alternately with the specific optimization for the needle, for fluid flows and/or possibly for tissues may be obviously selected.
Specific receiving, processing and storing chains, or a single chain which rapidly switches its characteristics for the various scan modes are enabled in a synchronized manner with the transmission of ultrasound beams having the specific optimized parameters for the needle, the fluid flows and/or possibly for tissues. The images obtained thereby may be then be processed and possibly combined together in any manner, to be further displayed and/or stored.
As an alternative, transmit parameters may be set in a memory and later recalled from the memory, in a manner that corresponds to the specific preset succession of scans, to control the scan according to the different parameters contained in the memory.
An additional variant embodiment provides memories both for transmit parameters and for receive parameters and possibly even for image processing and/or handling and combining parameters.
In this case, each specific setting of transmit parameters, univocally related to imaging optimized for the needle, body fluid flows and/or possibly tissues corresponds to a specific setting of control parameters for the processing chain and possibly to a specific setting of parameters for processing, handling and/or combining the images obtained with different modes for the needle, body fluid flows and/or possibly tissues.
The invention also relates to an apparatus for the implementation of said method, which comprises an ultrasonic probe, means for generating ultrasound beams and for controlling the scan of a body under examination by said ultrasound beams; means for receiving and reconstructing image data from the ultrasound beams reflected by the body under examination and display means, said apparatus being further provided with a memory in which the parameters for generating the ultrasound beams and for scanning the body under examination or a part thereof are loaded, which parameters are alternately optimized for imaging the needle and/or body fluid flows and/or possibly tissues, and means for receiving, reconstructing and processing reflected ultrasound beams deriving from said transmit beams, in a manner which is related to the parameters and scan modes with the transmitted ultrasound beams.
Advantageously, the apparatus includes a single chain for generating the ultrasound beams transmitted toward the body under examination or a part thereof, wherein the optimization of imaging parameters is controlled by means provided with a parameter setting memory, which is enabled according to enabling schedules which provide alternate scans with the different parameters.
In combination with the above, the apparatus includes one or more receive and processing chains, each dedicated to the simultaneous or successive handling of the data obtained by any type of imaging parameters.
In accordance with a variant embodiment, the apparatus includes a single chain for generating the ultrasound beams to be transmitted and/or for scanning and a single chain for receiving and processing, there being provided a central control unit, which is connected to the memories containing the parameters of transmitted ultrasound beams according to the different optimizations for imaging the needle and body fluid flows and/or possibly tissues, and to the memories containing the receive and processing modes dedicated to the reflection signals obtained with the particular optimized settings of parameters for imaging the needle and/or body fluid flows and/or possibly tissues, which control means access the memories according to an imaging time protocol based on the different parameters and, as a result, control the means for generating and transmitting the ultrasound beams, as well as the means for receiving, processing and/or handling images and/or possibly combining the individual images optimized for the needle and/or body fluid flows and/or possibly tissues.
The advantages of this invention are self-evident from the above disclosure and especially consist in allowing an optimized visualization of a biopsy needle in combination with an optimized display of body fluid flows and possibly of the tissues around the needle.
The whole is obtained in a fast manner, such as to allow real-time imaging, without imposing long waiting times on patients, and while maintaining short intervention times.
The better visualization of the biopsy needle and of fluid flows and/or tissues allows a more accurate positioning of the needle in the sample removal site, thereby ensuring a better reliability of diagnostic tests performed thereon, particularly when the sample removal site has a very small size, and tissue removal might easily occur outside it.
The visualization of body fluid flows allows a more accurate identification of the tissues of interest for sample removal, particularly in not completely degenerated conditions, or in initial stages of diseases like tumors or the like.
The possibility to combine the methods of the invention with other imaging methods, like three-dimensional imaging methods, or other methods, provides a maximized expansion and improvement flexibility.
Further improvements of the method and of the apparatus will form the subject of the subclaims.
The characteristics of the invention and the advantages derived therefrom will appear more clearly from the following description of a few non limiting embodiments.